It has been demonstrated that the immunologic potential declines in old age. We have found that aged mice develop large numbers of suppressor T cells following antigenic stimulation, and that their lack of immunocompetence can be ascribed in large part to the suppressor cells. We now plan to analyze the function and number of helper T cells and B cells as a function of age. In addition, we will investigate the interactions between B cells and T cells in young and old mice, and the mechanisms that render B cells from aged mice resistant to tolerance induction. BIBLIOGRAPHIC REFERENCES: M. Segre and D. Segre (1976). Humoral immunity in aged mice. 1. Age related decline in the secondary response to DNP of spleen cells propagated in diffusion chambers. J. Immunol. 116:731. D. Segre and M. Segre (1976). Humoral immunity in aged mice. II. Increased suppressor T cell activity in immunologically deficient old mice. J. Immunol. 116:735.